DESCRIPTION: Unlike retroviral vectors derived from simple retroviruses, lentiviral vectors stably transduce nondividing cells. This property has relevance to diseases as diverse as HIV disease, cystic fibrosis and neurodegenerative disorders, because it may permit therapeutic gene transfer to quiescent progenitor cells or post-mitotic cells in various organ systems. In addition to potential therapeutic application, efficient lentiviral vectors represent basic research tools with potential to enable novel strategies of basic biological investigation. Lentiviral vectors derived from nonprimate lentiviruses could provide attractive alternative to vectors derived from human immunodeficiency virus (HIV). However, species-specific blocks to infection and expression have made the feasibility of this option uncertain. Preliminary experiments show that pseudotyped feline immunodeficiency virus (FIV)-based lentiviral vectors efficiently transduced nondividing cells of diverse origin. The goal of this proposal is to obtain basic molecular knowledge about the FIV life cycle that is necessary for two purposes: constructing optimal FIV-based lentiviral vectors and understanding FIV disease as a model of AIDS pathogenesis. This goal will be achieved using tissue culture investigations to elucidate optimal FIV vector system design, and animal models to investigate gene transfer efficacy in vivo. The three specific aims are: (1) to study molecular requirements for optimal FIV-based gene transfer vectors. In particular, determinants of FIV genomic mRNA encapsidation (virion packaging) are unknown and require investigation. Mutational analysis of the FIV genome will be performed using direct measurements genomic mRNA encapsidation; (2) to study molecular requirements for optimal FIV packaging constructs. Maximal deletion of encapsidation determinants and other cis-acting sequences from packaging constructs will be pursued in experiments complementary to Specific Aim 1. Requirements for FIV Vif protein and FIV dUTPase will also be investigated. An outcome expected for Specific Aims 1 and 2 is a minimal FIV vector system; (3) to investigate the properties of FIV vectors in animal models. Two rodent models have been chosen for importance to gene therapy and for capacity to demonstrate lentivirus-specific properties: sterotaxic injection of rat and mouse brain and gene transfer to SCID repopulating cells in the NOD/SCID mouse. Expert collaborators have been secured for both animal models. Information obtained from studies described in specific aims 1 and 2 will be used to maximize efficiency of in vivo gene delivery in Specific Aim 3.